（71）The method of scientific investigation is nothing but the expression of thenecessary mode of working of the human mind;it is simply the mode by which allphenomena are reasoned about and given precise and exact explanation.There is nomore difference，but there is just the same kind of difference，between the mental operationsof a man of science and those of an ordinary person，as there is between the operations andmethods of a baker or of a butcher weighing out his goods in common scales，and theoperations of a chemist in performing a difficult and complex analysis by means of his balanceand finely graded weights.（72）It is not that the scales in the one case，and the balancein the other，differ in the principles of their construction or manner of working;butthat the latter is much finer apparatus and of course much more accurate in itsmeasurement than the former.

You will understand this better，perhaps，if I give you some familiar examples.（73）Youhave all heard it repeated that men of science work by means of induction（归纳法）anddeduction，that by the help of these operations，they，in a sort of sense，manage toextract from Nature certain natural laws，and that out of these，by some special skillof their own，they build up their theories.（74）And it is imagined by many that theoperations of the common mind can be by no means compared with theseprocesses，and that they have to be acquired by a sort of special training.To hear allthese large words，you would think that the mind of a man of science must be constituteddifferently from that of his fellow men;but if you will not be frightened by terms，you willdiscover that you are quite wrong，and that all these terrible apparatus are being used byyourselves every day and every hour of your lives.

There is a wellknown incident in one of Moliere’s plays，where the author makes the heroexpress unbounded delight on being told that he had been talking prose（散文）during thewhole of his life.In the same way，I trust that you will take comfort，and be delighted withyourselves，on the discovery that you have been acting on the principles of inductive anddeductive philosophy during the same period.（75）Probably there is not one here whohas not in the course of the day had occasion to set in motion a complex train ofreasoning，of the very same kind，though differing in degree，as that which ascientific man goes through in tracing the causes of natural phenomena.